Electrical igniter



March 26; 1935. w KlRsT 1,995,354

ELECTRICAL IGNITER Filed June 25, 1931 INVENTOR William Emmi PatentedMar. 26, 1935 PATENT OFFICE ELECTRICAL IGNITER William E. Kirst,Woodbury, E. I. du Pont de Nemours mington, Del., a corporation N. J.,assignor to & Company, Wilof Delaware Application June 25, 1931, SerialNo. 546,773

9 Claims.

My invention relates to means for igniting a fuel, preferably in liquidform, by electrical means, and more particularly to a means in which thecontinued application of a source of high temperature is applied becauseof the high flash-point of the fuel to be ignited.

Electrical ignition in the form of electric squibs has long been used inexplosives practice for igniting such compositions as black powder,where the explosive is initiated by the application of flame. In theelectric squibs used for this purpose, the ignition composition isusually contained in a small diameter tube of metal, cardboard or othermaterial, and the ignition of this composition is brought about by theuse of an incandescent electric wire embedded in it. Such a tube,orelectric squib, is placed so that the flame from the ignitioncomposition plays upon the black powder or other material to be fired.

The advantages of electrical ignition are, of course, apparent. Whenthis method is used in the case of explosives, for example, the exactmoment of firing can be predetermined so that all workers may be in aplace of safety at the time the explosion occurs.

taneously if necessary, or in any predetermined order with a consequentgreat saving in time.

I have now found that electric ignition means may with certainmodifications be used with particular advantages in the lighting ofso-called orchard heaters, which have a very extended use in theprotection of fruit and other crops against damage by frost. In suchfrost protection work, it is the practice to place vessels containingfuel oil or other combustible material spaced at definite intervals,throughout the region to be protected. When the fuel in these vessels isignited, the heat from the burning oil serves to keep the temperature ofthe air in the neighborhood of the fruit above the frost point. Beforethe present invention the method used to ignite the oil has consistedgenerally in the use of a torch, with which the workmen light one heaterafter another.

The methods of ignition heretofore used for this purpose have manyobjectionable features. In the first place, the lighting has beentimeconsuming. Either the first heaters are lighted earlier thannecessary, with consequent waste of fuel, or the last ones are lightedtoo late, with a possible loss of fruit. With an electrical ignitionprocess, however, the heaters can be wired previous to the time of useand the lighting will then be instantaneous at the desired moment.

Also by this means alarge number of ignitions can be effected simul- Itis also possible to connect the ignition devices in such a way as tofire them in certain unit lots, thermostatically controlled, if desiredby atmospheric temperatures. I

While my invention has been described in the foregoing as applied to thelighting of orchard heaters for frost protection purposes, it is to beunderstood that this is only one application of my invention, and thatsuch a process may be applied to other fields where fuel lights orheaters are utilized. For example, such a process is applicable to roadconstruction work Where it is necessary to place long stretches ofwarning lights for use at night. This, as will be apparent, would bringabout a considerable saving of time and fuel, as well as adding anelement of safety. A still further application of an ignition process,according to my invention, lies in the field of pyrotechnics, where theinstantaneous or simultaneous lighting of signals at many definiteplaces may be desirable.

While electric ignition means has been satisfactorily used heretofore inthe field of explosives, serious difiiculties have existed to preventthe satisfactory use of such means in other fields, such as thosedescribed in the foregoing. In the case of orchard heaters used forfrost protection, for example, it frequently happens that the vesselsare re-lighted, after previous use. In such a case, the fuel oil presentwill have a high flashpoint, or it may occur that a high flash-point oilis used in the first filling of the containers. Under such conditions,the ignition of the fuel by electrical means is very dimcult. In orderto ignite the oil, it is necessary that the heat be applied continuouslyand intensively to it. It is necessary also that the application of theheat be at the surface of the oil, as submersion of the flame will besufiicient to extinguish it. If, for example, the ordinary type ofelectric squib as heretofore used is applied, the flame gives offinsufficient heat for ignition. In addition, the squib is sufficientlyheavy so that it sinks below the surface of the oil.

I have now discovered a method of avoiding the disadvantages of theelectric ignition processes previously available. I find that a greatadvantage is obtained if means are used to keep the ignition device atthe surface of the fuel oil throughout the time of combustion of theignition composition.

This may be brought about in a number of ways. For example, a wick ofcanvas or asbestos may be used, to which the squib is attached, or inwhich it is wrapped. On continued mit the squib to be held tightly andsecured in:

place by friction.

By such a method, the maintenance of the squib at the surface of the oilis assured. Also, the squib will be kept 'inan upright position so that,at the time of ignition, thev flame will be directed downward toward thesurface of the oil or other liquid fuel. The ignition process is furtherfacilitated by the fact that the block of wood soon becomes saturatedwith the liquid fuel on continued contact with it, and consequehtly isreadily ignited. A still further advantage of this-arrangement lies inthe fact that the depression holding the squib forms a container for theintensely hot reaction products and thereby renders ignition morecertain. While various kinds of wood may be used for the block, in whichthe electric squib is inserted, I prefer to use a very low density woodsuch as balsa wood or cork.

I find that a still further advantage results if the block of wood, inwhich the squib is inserted, has been treated in a way to promotecombustion, preferably by impregnation with an oxidizing material. Whilevarious axidizing agents are satisfactory for this purpose, I findsodium nitrate a very desirable material, having the advantage of lowcost and suflicient available oxygen for promoting vigorous combustion.Various methods of bringing about this impregnation may be used, as, forexample, byuse of a more or less concentrated solution of sodiumnitrate, with subsequent drying of the impregnated block. I find asuitable degree of impregnation to be that which gives a dried blockhaving a 20-60 per cent content of sodium nitrate.

Even when a device such as the above is used, the described method ofignition is not uniformly satisfactory with the electric squibs nowcommonly used, because of the fact that the temperature of the flamefrom the ignition composition is not sufficiently high to ignite highflash-point oil, so that permanent combustion will take place. I havefound that this disadvantage may be overcome if a special type ofsquibis used, containing an ignition charge that burns with theevolution of an unusually large amount ofheat and produces at the sametime intensely hot liquid or solid reaction products. In this manner theheat is made available for ignition over a much longer period of time. I

I find that a squib having the desired igniting qualities is obtainedwhen a base charge is used consisting of a so-called alumino-thermicmixture, otherwise known as thermit. A satisfactory base charge isobtained, for. example, when a mixture of metallic aluminum and ferricoxide isused. I find a suitable composition to be obtained when thealuminum and ferric oxide are present, for example, in the amounts of 24and 76 per cent respectively.

This mixture, when once ignited, burns with an intense heat, sufiicientto ignite the oil-soaked wooden block in which the squib is inserted andsubsequently to ignite the fuel oil permanently.

As described in the foregoing, the inserting of the squib in the hole ofa wooden float offers an additional advantage in supplying a containerfor the white hot molten iron formed in case thermit is used. Such aretaining and localizing of the heat greatly increases the certainty ofignition.

While I have suggested for this purpose the use of ferric oxide, F9203,I may also use the magnetic oxide, FeaOa'. Similarly other oxidizingagents may be used in place of the iron oxides, but it is essential thatthe metal used be one having a high heat of combustion.

While a composition such as is described above will ignite the fuel oilsatisfactorily, the mixture itself is difficult to ignite. As anignition charge for the thermit, therefore, I prefer to use a morereadily ignitable composition, containing a metal and an oxidizingagent. For this purpose, I find a mixture of metallic magnesium andbarium peroxide to be satisfactory. This mixture gives sufficient heatto ignite the base charge, and may itself be ignited by an ordinaryignition charge such as is commonly used in electric squibs at thepresent time, or by the heat from an incandescent electric wire of theproper diameter. While varying proportions of these ingredients may beused, I find desirable results tobe obtained when the magnesium andbarium peroxide are present in the amounts of 12 per cent and 88 percent respectively.

By way of more specific illustration, my ignition means is shown invertical section in the accompanying drawing. Figure I shows thecomplete arrangement for carrying out the invention, in which Arepresents the container for the liquid fuel and B the fuel itself.represents a fioatmade of wood, preferably cut across the grain, orother combustible material adapted to float on the surface of the liquidand having a hole on the upper surface, into which the electric squib Dfits tightly, so that it is maintained in upright position, pointingdownward. When the squib is fired by electric current through theleading wires E, the hot non-gaseous reaction productsare held in thesquib hole, and the heat is suiiiciently intense to ignite theoil-saturated float, whereby the oil itself becomes permanently ignited.Figure II similarly illustrates the form of electric squib preferablyemployed, in which the base charge is represented by H and the ignitioncharge by I. When theelectriccurrent flows through the leading wires M,the bridge wire J becomes heated sufficiently to fire the ignitioncharge. A water-proofing composition K isused after the ignition charge,followed by the usual sulfur plug L at the top of the squib. Nrepresents the metal container for the entire squib.

While Ihave described the igniting means of the electric squib asincluding abridge wire, it will, of course, be understood that theso-called match-head, or electric spark may be used in place of thebridge wire.

Also, while I have described my improved process as an electricalignition process, it will be seen that the electric current does notactually bring about ignition of the fuel oil. It merely fires theinitial charge, the actual ignitionof the oil resulting from the intenseheat from the base chargein the squib.

While certain specificembodiments of my invention have been described indetail, it will be understood, of course, that other'embodiments existand maybe practiced; without departing 75.

from the spirit oi the invention, and that I do not intend to be limitedin my invention except as indicated in the following patent claims:

I claim:

1. An electric igniter for liquid fuel comprising in combination a blockof wood of lower speciflc gravity than the liquid fuel and an electricsquib inserted in said block of wood.

2. An electric igniter for liquid fuel comprising in combination a blockof wood treated in a way to promote combustion, said block being adaptedto float on the liquid fuel, and an electric squib inserted in saidblock of wood.

3. An electric igniter for liquid fuel comprising in combination a blockof wood impregnated with an oxidizing material, the block being adaptedto float on the liquid fuel, and an electric squib inserted in saidblock of wood.

4. An electric igniter for liquid fuel comprising in combination anigniter float, impregnated with an oxidizing material and capable ofabsorbing a substantial amount of the liquid fuel, to serve as a wickfor the fuel, and an electric squib attached to said float.

5. An electric igniter for liquid fuel comprising in combination a blockof wood impregnated with sodium nitrate, the block of wood being adaptedto float on the liquid fuel, and an electric squib inserted in saidblock of wood.

6. An electric igniter for liquid fuel comprising in combination a blockof wood containing 20-60 per cent of its weight of inorganic oxidizingmaterial, the block being adapted to float on the liquid fuel, and anelectric squib inserted in said block of wood.

7. An electric igniter for liquid fuel comprising in combination a blockof wood containing 20-60 per cent of its weight of sodium nitrate, theblock being adapted to float on the liquid fuel, and an electric squibinserted in said block of wood.

8. An electric igniter for liquid fuel comprising in combination a blockof wood that has been cut across the grain in such manner that it willact as an absorbent for the liquid fuel, the block being adapted tofloat on the liquid fuel, and an electric squib inserted in said blockof wood.

9. An electric igniter for liquid fuel comprising in combination a blockof wood that has been cut across the grain in such manner as to act asan absorbent for the liquid fuel, said block containing 20-60 per centof impregnated oxidizing material and being adapted to float on theliquid fuel, and an electric squib inserted in said block of wood.

WILLIAM E. ICIRST.

